Responding to Anson, the UK Revenue states it will continue to treat LLCs as opaque

HMRC ambiguously stated that the Anson decision "means that where US LLCs have been treated as companies within a group structure HMRC will continue to treat the US LLCs as companies."

I understand from a senior U.K. correspondent of Nat Boidman that the "treating" is by HMRC rather than the IRS. He notes that HMRC have long regarded US LLCs as "opaque" (see INTM180030, which is a country-by-country listing of entities as transparent or opaque for U.K. income tax purposes), and are effectively saying they will continue to do so.

Neal Armstrong. Summaries of [U.K] Revenue and Customs Brief 15 (2015): HMRC response to the Supreme Court decision in George Anson v HMRC (2015) UKSC 44 and INTM180030 - "Foreign entity classification for UK tax purposes: List of Classifications of Foreign Entities for UK tax purposes" under s. 248(1) – corporation.